Japanese experts check Thu Thiem Tunnel before it was officially open to traffic under the Saigon River on Sunday

The longest cross-river tunnel in southeast Asia, Thu Thiem, was opened to traffic across the Saigon River in southern Vietnam on Sunday.

A big ceremony with the Japanese International Cooperation Agency (JICA), which has invested in the project with ODA funds, technologies and consultancy, was held at the two ends of the tunnel.

The 1.49-kilometer tunnel can accommodate up to 150 cars and 300 motorbikes, or between 500 to 800 people at peak time. Thus, it is expected to reduce the traffic flow on the overloaded Saigon Bridge.

The tunnel also completes Ho Chi Minh City's major East-West Boulevard that runs 21.89 kilometers through many city's districts. People will save around 20 minutes traveling from the city to Mekong Delta destinations and areas to the east of the city, such as the the beach town Vung Tau.

Nguyen Van Nam, a 73-year-old local, said "I'm happy, as the tunnel will make it easier now for my children to go to work and school."

After the ceremony, around 2,500 people, including locals and officers, were arranged to travel through the tunnel.

Motonori Tsuno, chief representative of JICA, said at a press conference on Saturday that Thu Thiem was a big and meaningful project to HCMC, Tuoi Tre reported.

Director of the Japanese consultant firm Oriental told the press that the tunnel has been designed with optimum technologies for 100 years of use.

But the JICA representative also said that Vietnam needs to regularly maintain the tunnel, and to be strict not to let overloaded vehicles travel through the tunnel, to keep it in good shape for 100 years.

Local experts have warned of possible fire and explosion hazards inside the tunnel, where it would be difficult for people to escape.

But Japanese units have ensured that they will handle problems for one year, before transferring the management and technologies to Vietnam.

The Japanese contractors said their Vietnam counterparts are now capable of working on a similar project.

Thu Thiem tunnel took nearly seven years to build. The tunnel was constructed in four sections in Dong Nai province, neighboring Ho Chi Minh City, and completed in September 2010. After the sections were completed, they were moved to the tunnel location under the Saigon River and joined. Each section is 92 meters long and weighing more than 27,000 tons.

Le Toan, deputy director of HCMC Transport Department, said that although Thu Thiem, or the whole boulevard project, changed the life of locals as well as the look of the city, people seem to be content with the project.

Toan said a total of 6,744 households and 368 government and business agencies were relocated during the US$762 million project, likely the biggest relocation project in the city.

"But there've been no public complaints that have slowed down the project," he said. "The project has improved the life of thousands of people living along ditches and canals moving them to better residential areas," Toan said, cited by Tuoi Tre.

He also said in the city downtown, many bridges such as Calmette and Khanh Hoi were rebuilt, while narrow two-lane streets such as Ben Chuong Duong, Ben Ham Tu and Tran Van Kieu were merged into the boulevard, which has eight to 14 lanes.